1. Technical Field
The invention relates to a bushing, in particular a plain bearing bushing, with cylindrical lateral surface, which is formed from a material strip such that in circumferential direction two joining ends are arranged adjacently, wherein, at a first joining end, is arranged a projection and, at a second joining end, is arranged a recess engaging in formfitting manner with the projection.
2. Related Art
Such bushings have been known for a long time and are used in the most diverse technical areas. By way of example for the state of the art the documents DE 3511125 A1, DE 3316767 A1, U.S. Pat. No. 1,298,100, EP 1248005 B1 or the WO 2007/087771 A1 are stated.
As standard, bushings are manufactured by forming processes, in particular rolling or bending, of a material strip. At that, the two joining ends of the material strip have interlocking elements corresponding to each other that are moved towards each other in a tangential way during the forming process and eventually are interlocked with each other. The joining ends mark the sides of the material strip between which a butt joint is formed after the forming process. Typically, an interlocking element in form of a journal is configured with undercuts and the other interlocking element in form of a recess with which the journal engages for axial and circumferential fixation. These interlocking elements are not exactly complementary at the beginning of the forming process. The joining end with recess rather has small tails firstly on one side or on both sides of the recess, folded into the undercuts of the journal when journal and recess are pushed into each other, creating a formfitting fixation of the joining ends in circumferential direction, which is called a “clinch connection.” During folding the materials is formed.
In addition, interlocking elements are known with which the journal has a larger extension in circumferential direction of the bushing than the complementary recess that in turn is configured wider in axial direction of the bushing than the corresponding journal. This is described for example in U.S. Pat. No. 2,283,918. When journal and recess are pushed into each other, the journal first is clinched as soon as it touches the edge area of the recess opposite the opening of the recess. When the joining ends are further moved towards each other, the clinched material evades in axial direction into the space between the journal and recess, creating further undercuts. Thus, a formfitting connection of the joining ends results in circumferential direction of the bushing as well.
In both cases described, a formfitting connection, a clinch, results from material forming processes. These methods of bushing production by way of material forming process do have the disadvantage that the accuracy of the form fit depends substantially on material flow during joining. Practical experience has shown that not in all cases a suitable form fit can be achieved, which in certain cases results in loosening of the interlocking elements and thus in the entire bushing yielding in the bearing bore. In order to reduce this risk, stricter controls of the interlocking elements are required, which increases both rejects and production costs of the bushing.
Similar interlocking elements that are subject to a material forming process during joining are also known from other technical areas. By way of example, specifications U.S. Pat. No. 7,025,393 B2 or U.S. Pat. No. 7,794,609 B2 are referred to.
To overcome the issues described, bushings with smooth joining ends or at least joining ends without undercuts are used for very precise applications with low dimensional tolerance. Such bushings, for example, are known from EP 0 218 274, DE 198 37 596 C1, DE 28 18 378 A1 or U.S. Pat. No. 4,909,638. With these bushings the interlocking elements are arranged exactly complementary to each other. This results in these interlocking elements engaging with each other in a formfitting manner even without any material forming process. This kind of interlocking, however, has the disadvantage that due to the exactly complementary interlocking elements very close production tolerances must be observed during the forming process to avoid damage to the journal or the recess and any resulting reject of the bushing. Another disadvantage results from the formfitting fixation of the joining ends only in axial direction of the bushing and thus no creation of a clinch connection. Thus there is no formfitting fixation in circumferential direction of the bushing. Consequently, it will not be possible to close the bushing without a gap, which makes any subsequent processing and the installation in the respective bearings very difficult.
From specification DE 40 19 055 C1 another bushing with interlocking elements in the form of wedging projections and recesses is known, the wedge angle of the wedge surfaces capable of being engaged with each other being larger than the self-retaining angle. The wedge angles thus have deliberately been chosen in a way to ensure that the bushing is able to expand radially outwards.
Accordingly, this is a bushing that cannot be closed without a gap either. Against this background, it is the objective of the invention to provide a bushing that mostly overcomes the disadvantages of the state of the art.